The invention relates generally to systems and methods which facilitate fallopian tube occlusion.
In the United States, approximately 600,000 to 700,000 women undergo the form of sterilization known as laparoscopic tubal ligation each year. This frequent procedure typically involves general or regional anesthesia in an outpatient setting. A small incision is made through the xe2x80x98belly-buttonxe2x80x99 and also above the pubic bone. Thereafter, electrical forceps, a pair of clips or rings, are then applied to the isthmic portion of the fallopian tubes which usually results in closure.
The history of hysteroscopic fallopian tube occlusion is long and extends back to at least 1849, when Froriep tested a silver nitrate solution. Since then, many investigators have researched human fallopian tube occlusion utilizing transvaginal, transcervical, and transuterine (TVCU) approaches which can be divided into either (i) destructive-obstructive methods, or (ii) mechanical-obstructive methods. Both of these methods, however, were performed in a xe2x80x9cblinded fashionxe2x80x9d, meaning that the operator was unable to visualize or identify the internal length of the tube, even though the beginning of the fallopian tube, i.e., the tubal xe2x80x9cfunnelxe2x80x9d, was visualized or palpated.
In the destructive-obstructive methods, for example, various caustic substances, including quinacrine and more recently methyl 2-cyanoacrylate (MCA), have been tested and utilized with varying degrees of success to damage, and hence close, the fallopian tube. MCA, for example, is delivered without anesthesia in an outpatient setting. A balloon device pushes the MCA from the uterine cavity and, if all goes well, through both fallopian tubes. Little substantive clinical data is however available to evaluate safety issues and the complication rates associated with such methods.
Other such destructive methods which attempt to damage and close the intramural portion of the fallopian tube include heat, electosurgery, and laser illumination. These methods have not gained acceptance due to (i) high failure and complication rates, (ii) the necessity of general or regional anesthesia, and (iii) the high cost and need for a skilled hysteroscopist. See, e.g., Zatuchini, Contraceptive technologies for the future, Current Problems in Obstet and Gynecol, 7(11) (1984).
Similarly, the mechanical-obstructive methodology for obstructing the human fallopian tube have been tested, for example, with either silastic or metal plugs. The effectiveness of these mechanical methods, however, is typically no better than those occlusion methods which attempt to destroy the fallopian tube.
In 1985, Platia and Krudy reported the first successful TVCU catherization, under hyserosalpingographic (HSG) guidance, of a suspected obstructed fallopian tube in an infertile woman, and which resulted in a subsequent pregnancy. They utilized a 3 Fr., end hole polyethylene catheter with a 0.018xe2x80x3 pediatric guide wire. M. Platia and A. Krudy, Transvaginal floroscopic recanalization of a proximally occluded oviduct, Fertil and Steril, 44(4):704 (1985). This technique is now routinely utilized to treat certain types of tubal obstructions.
In 1988, a bi-polar radiofrequency catheter was developed which produced an obstructing lesion in the isthmic portion of the human falopian tube. This first generation catheter had two 1 mm electrodes separated by 1 mm. Utilizing the cat-uterine horn, a lesion of less than 1 cm was produced with inconsistent closures. A subsequent, second generation catheter bad two 3 mm electrodes separated by 3 mm. This resulted in a lesion of approximately 1 mm to 1.5 mm per electrode. Although there appeared to be closure, there was microscopic, histologic recannalization of the fallopian tube obstructing lesions. These recannalization effects raise questions concerning the occlusion efficacy and consistency using this technique.
Improvements in fallopian tube occlusion are thus sought. to improve cost effectiveness, patient safety, and reliability. For example, the widely used laparoscopic tubal ligation still has a sterilization failure rate of approximately 0.2 to 0.6%. DeStefano et al., Demographic trends in tubal sterilization: United States, 1970-1978 AJPH, 72(5), 480-484 (1982); Greenspan Jr. et al, Tubal sterilizations performed in freestanding ambulatory-care surgical facilities in the United States in 1980, J of Reproductive Medicine, 29(4), 237-241 (1984).
It is, accordingly, an object of this invention to provide improved methods for fallopian tube occlusion. Other objects of the invention will be apparent from the description which follows.
In one aspect, the invention provides a method for noninvasive transcervical tubal occlusion (sterilization) in women. A sterilization catheterxe2x80x94designed to be introduced in a transcervical-transuterine fashionxe2x80x94is passed into the fallopian tube either under direct visualization with a fiber optic system such as the Linear Everting Catheter (Imagyne), or fluoroscopically using standard radiologic-angiographic techniques. A microwave energy source (e.g., operating at 915 MHz) connects with an antenna contained within a disposable catheter. The catheter preferably has a diameter of approximately 2-3 mm, or smaller. The microwave antennas can be reused, but are preferably inexpensive so as to be disposable after one treatment. The treatment time (i.e., the time the energy is delivered) is approximately ten minutes. The latent period to fallopian tube occlusion is approximately 45-60 days.
In another aspect, the invention provides a system which produces sterilization through closure of the fallopian tube. The system elevates the temperature of living tissue through absorption of microwave energy. The system transfers microwave energy from a generator outside the body to the site of heating without significant deposition of energy in tissue. Preferably, the system incorporates a coaxial cable to facilitate the energy transfer. In one aspect, the applicator utilizes a monopole conductor extending from the coaxial cable and embedded in a cylinder of insulating, biocompatible material, such as polytetraflouroethylene (Teflon). Accordingly, at the heating site, the applicator couples microwave energy to the surrounding tissue without direct contact between a metal conductor and the tissue
At the site of intended heating, the oscillating current and charge in the monopole conductor produces oscillating electric and magnetic fields in the surrounding tissue. The oscillating electric field causes polar molecules in tissue, such as water, to rotate in place, generating frictional heating. The presence of an overlying layer of insulating material does not prevent the formation of electric and magnetic fields in tissue, because the length of the monopole is chosen to form a resonant (or near-resonant) structure. Such a structure coordinates the electric and magnetic fields so that they sustain themselves outside the applicator. The length of such a structure is inversely proportional to the microwave frequency and is inversely proportional to the square root of a weighted average of the permittivity of the insulating layer and the surrounding tissue. For example, at 915 MHz or 2450 MHz (MHz=106 cycles/second), the length of the insulated monopole at resonance (or near-resonance) in tissue is one centimeter to several centimeters. The given values of microwave frequency are preferably those permitted by the FCC for use in industrial, scientific, or medical applications (e.g., ISM frequencies).
At frequencies less than microwave frequencies, e.g., less than 100 MHz, the length of a resonant structure is impractically long for use in the human body. Consequently, a low-frequency device, such as a radio-frequency device, must instead incorporate a metallic conductor in direct contact with tissue to permit the flow of a conduction current, which heats tissue through the translational motion of dissolved ions in tissue, not though the rotation of polar molecules. The intense conduction currents produced at the surface of a metal conductor in contact with tissue cause charring of tissue and hence poor control of the heating process. The invention thus avoids these problems.
In one aspect, the invention provides methodology which elevates the temperature of the fallopian tube in an out-patient procedure in order to produce biological responses that will cause the tube to close, preventing future pregnancy. An insulated, microwave applicator is inserted through a transvaginal-transcervical-transuterine technique so as to place the applicator tip in the fallopian tube. Microwave energy is applied to the external end of the applicator to heat fallopian tube tissue surrounding the tip. In testing of animals, it has been shown that 35 watts of microwave power at 915 MHz elevates the temperatures at the hottest point to approximately 65xc2x0 C. for approximately 5 minutes. After four to six weeks, examinations show that the architecture of the uterine tissue is completely effaced at the point of maximum temperature and the lumen is closed on both sides of this region.
In one aspect, the invention provides a method for non-invasive occlusion of a fallopian tube, including the steps of: inserting an assembly of electrical conductors into the fallopian tube, the conductors forming a microwave antenna; and driving the conductors with microwave frequencies wherein the antenna emits microwave radiation that heats the fallopian tube for delayed occlusion of the fallopian tube. In a preferred embodiment, the conductors is replaced by a single monopole such as formed by a center conductor of a coaxial cable.
The method can include the further step of shielding the conductors within a distal end of a biocompatible catheter to prevent direct contact between the conductors and tissue.
Preferably, the method includes visualizing placement of the distal end within the fallopian tube through an imaging catheter during the step of inserting. Alternatively, the method can include fluoroscopically estimating placement of the distal end within the fallopian tube during the step of inserting.
Acceptable frequencies of the invention include ISM frequencies such as 915 MHz and 2450 MHz.
The step of driving typically extends for approximately five minutes; and the delayed occlusion generally occurs between approximately 30 and 60 days.
Preferably, the step of inserting the conductors includes inserting a distal end of a coaxial cable. The center conductor of the coaxial cable forms a monopole conductor which extends from the distal end of the coaxial cable for a length corresponding to a desired resonant frequency.
Typically, the method includes the step of depositing one to ten watts of microwave power in the fallopian tube (and preferably within the isthmic portion of the tube).
The method can also include the step of heating tissue within the fallopian tube to between approximately 60 and 80 degrees C. for approximately two to ten minutes.
For purposes of control, the method can include the step of measuring tissue temperature during the step of driving the conductors. A microwave-immune thermometry catheter can be used for this purpose.
The invention also provides a system for occluding the fallopian tube. An elongated catheter has a distal end for placement into the fallopian tube, and a proximal end for manipulating the catheter. An assembly of conductors, disposed within the distal end of the catheter, deposits microwave energy into tissue of the fallopian tube without physical contact between the conductors and the tissue. The microwave energy heats the tissue for subsequent tubal occlusion.
Preferably, the catheter has a diameter between about 1-3 mm. The catheter can be disposable or non-disposable after one use; and is preferably formed of a biocompatible material such as Teflon.
In one aspect, the system includes a choke attached proximal to the conductors to reduce currents flowing from the distal end back towards the proximal end of the catheter. Such a choke can include a cylindrical conductor surrounding an outer shield of the coaxial cable and separated from the shield via an insulating layer. The cylindrical conductor has a distal end positioned towards the distal end of the catheter and a proximal end positioned towards the proximal end of the catheter. A connector electrically connects the cylindrical conductor to the shield at the distal end of the choke.
Alternatively, the choke includes a cylindrical conductor surrounding an outer shield of the coaxial cable and separated from the shield via an insulating layer; the cylindrical conductor has a distal end positioned towards the distal end of the catheter and a proximal end positioned towards the proximal end of the catheter, and a connector electrically connects the cylindrical conductor to the shield at the proximal end of the choke.
In another alternative arrangement, the conductors can include one end of a center conductor of a coaxial cable, and a ground plane attached to the outer conductor of the cable and deployed in the uterous connected with the fallopian tube to reduce currents flowing from the distal end back toward the proximal end of the catheter. The ground plane can for example be formed of wires separated by less than a wavelength of the energy so as to approximate a solid ground plane effect.
These and other aspects and advantages of the invention are evident in the description which follows and in the accompanying drawings.